In recent years, the internal quantum efficiency of an organic electroluminescence element (organic EL element) reaches almost 100%. On the other hand, the light-extraction efficiency relating to the external quantum efficiency remains at a level of from about 20 to about 30% and is required to be improved. As one reason why the light-extraction efficiency decreases is that part of light generated in an emissive layer located between two electrodes is lost in the element by reflection in the element, the surface plasmon, the guided waves, etc.
Patent Document 1 discloses a technique such that nanosized porous silica particles are incorporated in a charge transport layer to lower the refractive index of the charge transport layer thereby to improve the light-extraction efficiency.